Leuco compounds of vat dyes and process of making same.



UNITED STATES PA ENT OFFICE.

GADIENT ENGI, OF BASEL, SWITZERLAND, ASSIGNOR TO THE FIRM OF SOCIETY OF CHEMICAL INDUSTRY IN BASLE, OF BASEL, SWITZERLAND.

LEUCO COMPOUNDS OF VAT DYES AND PROCESS OF MAKING SAME.

Specification of Letters Patent.

Patented July 14:, 1908.

Application filed January 9, 1907. Serial No. 351,445.

836309, dated November 20th, 1906, No.

941003, dated January 8th, 1907, No. 848354, No. 848355, and No. 848356, dated March 27th, 1907, I have described a series of vatdyeing dye-stuffs and their halogenated derivatives, which derive from the alicylthioacetic acid s cn coon 1 oooH '2 and can be obtained by heating the said salicylthioacetic acid alone or mixed with an isatin compound as for instance isatin and alphaisatinarylides, in presence of a convenient solvent or condensing agent, as nitrobenzene or acetic anhydrid and treating the resulting dyestuifswhen a transformation in halogenated derivatives is desired-with a halogen as for instance bromin. I have now found that these vat-dyeing dyestuffs be-v longing to the group of thioindigo, which contains all the atomic complex in combination with the rest of an alpha'oxy-,

thionaphthene derivative or of an isatin compound and corresponding consequently to the general formula drosulfid and by precipitating the so formed leuco-compoundafter the alcohol has been distilled offby means of diluted hydrochloric acid in form of colorless small crys tals. By washing these latter and transforming the same into a paste, the new leucoderivatives are obtained directly in a form suitable for their technical use.

The invention is illustrated by the following example: 2 parts of the dyestuff obtained by brominating the product resulting from the condensation of equimolecular proportions of salicylthioacetic acid and isatin and corresponding probably to the formula:

are boiled up with 40 parts of alcohol; then 4 to 5 parts of a potassium hydrosulfid (KHS) solution of 25 per cent. are added to the mass and this latter boiled for some-time in a reflux ap aratus, whereby a clear, bright-yellow so ution is formed. After the greatest part of alcohol has been distilled off the mass is diluted with water and acidulated with hydrochloric acid, whereby the leuco-derivative precipitates in the form of colorless crystals, which are separated by filtration, Washed and transformed into a paste of the desired strength.

In an analogous manner the other dyestuffs belonging to the thioindigo-group, as for instance the thioindigo red,

s s o H, c=o o,H,, the products of condensation of salicylthioacetic acid with alphaisatin arylids S o=c compounds in dilute causticalkalies the vatdyeing dyestuffs fromwhich they are derived, can be precipitated in form of flecks, by the action'of the oxygen of the air or by'adding oxidizing agents.

' What I claim is:

1. The herein described process for the manufacture of leuco compounds of vat dyeand corresponding to the general formula which process consists in treating the said dyestuffs in an alcoholic suspension with alkalihydrosulfids andisolating the formed leuco compounds by acidulating the mass of reaction.

2. As new products the herein described leuco compounds derived from vat dyestuffs of the thioindigo-group constituting in a dry state colorless to yellowish-gray crystalline 15 powders, insoluble in pure water but soluble in alcohol and benzene with a light-yellow to brownish-yellow color, dissolving in dilute caustic alkalies with a brownish-yellow color from which solutions by the action oi the oxygen of the air or by adding oxidizing 2 agents the original vat-dyeing dyestufls sep arates in the form of flecks.

In Witness whereof I have hereunto signed my name this 19th day of December 1906,

in the presence of two subscribing witnesses. of

GADIENT ENGI.

Witnesses GEO. Grrronn, AMAND BITTER. 

